1. Field of the Invention
The present invention relates to an apparatus for playing back recorded information from an optical card which is used to read out (play back) information recorded on a card-shaped information recording medium (hereinafter, referred to as an "optical card").
The invention also relates to an optical card recording apparatus which is used to record information onto an optical card and, more particularly, to an optical card recording apparatus having a discriminating function to see if a defect such as a scratch or the like exists on information recording tracks of the optical card or not.
2. Prior Art Statement
In an optical system of a conventional optical card information playing back (reproducing) apparatus, as shown in FIG. 12, a light beam for reproducing recorded information is projected from a light source 1 for light projection such as laser, light emitting diode or the like. This light beam is converted into the parallel light beam by a collimator lens 2. The light beam is then converged by a condenser lens 3, thereby forming a light spot 6 onto an information recording portion 5 (refer to FIG. 13) on an optical card 4. The reflected light of the light spot 6 from the information recording portion 5 passes through the condenser lens 3, a reflecting mirror 7, an image forming lens 8 and the like and is finally received by a photo detector 9 consisting of a photo diode. Thus, a signal indicative of the information recorded on the optical card 4 is reproduced.
The information recording portion 5 on the optical card 4 is constructed by forming an information recording layer 11 on a substrate 10 and by further forming a transparent protective layer 12 on the information recording layer 11. As shown in FIG. 13, on the information recording layer 11, a number of pits 15 indicative of recording information are respectively formed in a line on each of a number of information recording tracks 14 formed along track guides 13. The track guides 13 are formed for controlling an optical head so as to trace the information recording tracks in the recording or reproducing mode (that is, they are provided for a tracking control).
A reflectance of pits 15 differs from reflectance of the other portion. As shown in FIG. 14a, in the case of an optical card in which the reflectance of the pits 15 is lower than that of the other portion, the level of the photo sensing signal from the photo detector 9 decreases in the portions of the pits 15 (FIG. 14b). By binarizing the photo sensing signal level on the basis of a threshold value V.sub.TH, binary data as shown in FIG. 14c is derived.
In the case of an optical card in which the reflectance of the pits 15 is higher than that of the other portion as shown in FIG. 15a, the level of the photo sensing signal from the photo detector 9 increases in the portions of the pits 15 (FIG. 15b). By binarizing the photo sensing signal level on the basis of the threshold value V.sub.TH, binary data as shown in FIG. 15c is derived.
When information is recorded onto the information recording tracks 15 of the optical card 4, the presence or absence of recorded information needs to be checked by previously scanning the information recording tracks 14 so that information is not overlappingly written at the same position. This checking process is performed by irradiating a light beam for reproducing the recorded information onto the information recording track 14 to be checked and by scanning this track. According to a recording method shown in FIG. 14a, the number of times when the level of the photo sensing signal is lower than the threshold value V.sub.TH is counted by the binary data. On the other hand, according to a recording method shown in FIG. 15a, the number of times when the level of the photo sensing signal exceeds the threshold value V.sub.TH is counted by the binary data. When each of the count values is 1 or more, it is determined that information is recorded on the information recording track 14.
However, the optical card 4 is not always in the proper ideal state and there is a case where defects such as scratches, fouling or the like exist on the information recording tracks 14. When such defects exist, although no recorded information exists, a misjudgement such that "the recorded information exists" is made, or in spite of the presence of the recorded information, a misjudgement such that "there is no recorded information" is made.
FIG. 16a shows a state in which in the recording method of FIG. 14a in the case where the reflectance of the pits is set to be lower than that of the other portion, a fouling Q is deposited on the portion where no recorded information exists on the surface of the optical card 4. In this case, the level of the photo sensing signal decreases in the portion of the fouling Q (FIG. 16b). When this level is binarized on the basis of the threshold value V.sub.TH, the binary data similar to that in the case where the recorded information exists is derived as shown in FIG. 16c.
On the contrary, FIG. 17a shows a state in which in the recording method of FIG. 15a in the case where the reflectance of the pits 15 is set to be higher than that of the other portion, a fouling Q is deposited on the portion where recorded information (pits 15) exists. In this case, the level of the photo sensing signal does not sufficiently rises in the portion of the fouling Q (FIG. 17b). When this level is binarized on the basis of the threshold value V.sub.TH, the binary data similar to that in the case where no recorded information exists is derived as shown in FIG. 17c (in other words, the signal level is always at the low level).
As mentioned above, in spite of the absence of the recorded information, if it is decided that the recorded information existed, this information recording track cannot be used any more, so that this causes a recording capacity to be reduced. On the contrary, in spite of the presence of the recorded information, if it is determined that no recorded information existed, information is overlappingly recorded on this information recording track, so that a defective recording of the information is performed.
The foregoing system detects only the presence or absence of the recorded information but does not actively detect defects due to scratches, deposited matters or the like on the surface of the optical card.
In the optical card 4 with the construction shown in FIG. 13, when defects due to scratches, deposited matters or the like exist in the information recording portion 5, after information was written onto the information recording tracks 14, even if this recorded information is played back, it is difficult to obtain the proper reproduced information.
Therefore, hitherto, when the optical card 4 is manufactured, an inspector checks the presence or absence of defects such as scratches or the like by observing the surface of the information recording portion 5 by the eyes, or the presence or absence of defects or an amount of defects is examined by scanning each of the information recording tracks 14 of the optical card 4 by using an optical head.
However, according to the former checking method by the observation using the eyes, the inspecting precision is low and it is difficult to detect such microdefects that can be hardly checked by the eyes. On the other hand, according to the latter detecting method, since it takes a long time to check one optical card, the manufacturing cost of the optical card increases. In any of these methods, moreover, it is impossible to cope with defects which may occur after the optical card was shipped.